Hydrothermal synthesis and automotive exhaust catalytic performance of CeO2 nanotube arrays

Abstract

Ceria (CeO 2 ) nanotube arrays with precisely defined size and density were directly synthesized on glass and cordierite substrates using a ZnO nanorods-assisted hydrothermal method. Eliminating the procedures of template removal and film coating, the one-step synthesis approach could greatly broaden the applications for materials with tubular structures. The proper concentration of cerium nitrate precursor solution acts a vital role to adjust the instantaneous precipitation of CeO 2 and dissolution of ZnO templates. The as-prepared CeO 2 tube arrays were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) techniques, which reveal a regular tubular structure with the average diameter of 500 nm and length of 3 mm. The automotive exhaust catalytic performance of CeO 2 tube arrays prepared on the cordierite was evaluated. Compared with the ceria nanoparticles film, the target CeO 2 tubes exhibit improved catalytic activities at a low start-up temperature for oxycarbide and hydrocarbon. Furthermore, the palladium-decorated CeO 2 tubes exhibit a higher catalytic activity for the degradation of oxynitride than that of palladium/ceria particles/cordierite.

Sacrificial template synthesis of high surface area metal oxides. Example: An excellent structured Fenton-like catalyst

“…A scheme of this mechanism is shown in Figure 1. This is a similar mechanism to that proposed by Feng et al [20].…”

“…Thus, its main advantage over other classical hard templating approaches is that there is no need for a template removal step. Initially used for the synthesis of Fe 2 O 3 nanostructures with a high lithium-ion storage capacity [13][14][15] STAH has also been applied in the preparation of platinum and palladium nanotubes for electrocatalysis and chemical sensing [16,17], NiO-based electrodes [18,19], CeO 2 nanotubes [20], and active electrocatalysts consisting of mixtures of noble metal nanotubes [21]. The common feature of all these publications is that the ZnO template is made up of nanowires or nanorods and the metal oxides obtained are in the form of nanotubes, with the exception of the ZnO-α-Fe 2 O 3 nanosheets described by Qin et al [14], which have a higher specific surface area (27 m 2 g -1 ) than nanotube-based materials.…”

“…It follows from this that metal oxide nanotubes are only produced from non-polar ZnO nanowires. It should also be noted that when Fe 3+ is used as precursor (a strongly acidic cation) the STAH reaction occurs readily at ambient conditions over the non-polar ZnO nanowires [13][14][15], whereas when much less acidic cations are used, such as Ni 2+ [18] or Ce 3+ [20] more drastic conditions are needed to produce the nanotubes. Only when the more polar ZnO is used is it possible to obtain ZnO-α-Fe 2 O 3 nanosheets at ambient conditions with mildly acidic cations (Fe 2+ ) [14], although up to now there has been no report in the literature on the synthesis of pure metal oxides with polar ZnO.…”

“…Only when the more polar ZnO is used is it possible to obtain ZnO-α-Fe 2 O 3 nanosheets at ambient conditions with mildly acidic cations (Fe 2+ ) [14], although up to now there has been no report in the literature on the synthesis of pure metal oxides with polar ZnO. This suggests that, contrary to what Feng et al affirm [20], the nucleation of metal oxides is not prevented on the polar faces by an electrostatic effect, but by the increased rate of dissolution of the polar faces due to the high acidity of the metallic cations (Fe 3+ ). On the other hand, when the metallic cations are less acidic, as in [14], the polar surfaces can be partially substituted by metal oxides.…”

Nano-Array Catalysts for Energy and Environmental Catalysis

“…The monolithic nano-array catalysts also showed excellent mechanical properties with well-retained morphology under both static (50 L min −1 ) and pulsatile (60 L min −1 ) air flow. Similar results were also obtained by Wang and coworkers on CeO 2 NTA-based catalysts [11]. The morphology change and weight loss of CeO 2 NTA were observed after 800 °C thermal annealing and the long time air flushing.…”